The present invention relates to a method and device for calibrating a regulated flow spraying apparatus and such a spraying apparatus. The invention is particularly useful for spraying fluids, namely in the field of agriculture.
Fluid spraying apparatus are already known comprising one or more sized orifices or nozzles having a flow rate regulated as a function of at least one external parameter, for example, the speed of the vehicle on which the nozzles are mounted. In this way the amount of fluid sprayed per unit surface area may be maintained at a predetermined value.
It is already known to regulate the flow rate of nozzles by adjusting the pressure of the liquid. Indeed, for values of pressures and flow rates used in such applications the flow rate q and the pressure p of the sprayed fluid are related with good accuracy by an equation of the form q=kp.sup.x. In this formula the exponent x is generally equal to 1/2. The coefficient k depends on numerous parameters and in particular on the geometrical characteristics of the spray nozzles and the properties of the sprayed fluid, for example its viscosity.
In known methods for regulating the flow rate of the sprayed substance by adjusting the pressure, the coefficient k called the "calibration parameter" in the rest of the specification is introduced by the user who thus determines the regulating equation.
The introductio or insertion of the calibration parameter by the user may be carried out explicitly. In this case the user takes the value of the calibration parameter from tables or graphs furnished by the manufacturer of the nozzles or determined by trial and error. The introduction or insertion of this parameter may also be determined implicitly when the apparatus comprises a calculator which determined the calibration parameter as a function of the size of the nozzles, the flow rate, the pressure, the viscosity and the density being given.
In all these cases the calibration parameter is determined at given point in time in conditions deemed representative of the operational spraying characteristics. These conditions are obviously not complied with, and sometimes are not even remotely close. Thus, the viscosity and density of the fluid may vary considerably, especially when the temperature varies. Further, the nozzles corrode gradually whereby their actual size varies.